In June 2017, the Office of Inspector General announced a review of the Federal Aviation Administration’s (FAA) oversight of air carrier maintenance. Based on our initial audit work and additional congressional requests, we are adjusting the scope of this audit. Our objectives now are to assess FAA’s processes for investigating allegations of improper maintenance practices at two carriers, Allegiant Airlines and American Airlines. Specifically, we will (1) examine FAA’s independent reviews, complaints to the FAA hotline, and other sources to see whether inspectors conducting routine surveillance of Allegiant and American Airlines found similar discrepancies and (2) determine whether FAA ensures that Allegiant and American Airlines implement effective corrective actions to address the root causes of maintenance problems.